In 2016, the Tromp family fled their home and drove 800km north. We still don't know why.

If you are struggling with your mental health, crisis support is available 24 hours a day via Lifeline. Please call 13 11 14.

When Victorian Police arrived at the Tromp family‘s home in Silvan, Victoria, on August 30, 2016, they found the doors unlocked. A station wagon was missing, but other cars had been left behind. The keys still in the ignitions.

Passports, mobile phones and bank cards belonging to the family of five were discovered inside, along with piles and piles of financial and business documents. They were neat and ordered, almost as if someone had been searching for something, police told The Daily Telegraph.

By then, the Tromps — Mark, 51, his wife Jacoba, 53, and their three adult children, Riana, 29, Mitchell, 25, and Ella, 22 — were already hundreds of kilometres into a journey that would spark one of the most bizarre missing persons cases in recent Australian history.

All five Tromps were ultimately located over the course of the next several days in various locations across NSW and Victoria. All were safe, but not all well.

The details of the case remain murky, pieced together from information provided by police and cryptic press conferences later given by Mitchell and Ella in an effort to satisfy the baffled press and public.

It was confirmed, via Riana’s 2017 interview with Woman’s Day, that a build up of stresses had led to her father suffering a mental breakdown. One so intense that he feared someone was after him and prompted him to flee.

But many questions remain unanswered, including the key one: why did the rest follow? Why, on August 29, did an entire family suddenly pile into Ella’s silver Peugeot wagon and head north, with little on them but a pile of cash?

The timeline.

Monday, August 29.

The family fled their Silvan home and drove toward NSW.

About 32km into the journey, Mitchell’s mobile phone, believed to be the only one brought on the trip, was thrown out the car window near Warburton, reportedly amid fears it could be tracked.

Tuesday, August 30.

Around 7am, Mitchell, frustrated by his parents paranoia, abandoned the trip near the regional NSW town of Bathurst and began the journey back home via Sydney.

A short time later, the rest of the family arrived in Jenolan Caves, near the Blue Mountains, where the two sisters then stole a car and drove back south to Goulburn. There, they went their separate ways.

Ella continued the drive on to Silvan, while Riana was found that afternoon in the back of a stranger’s ute, in which she’d attempted to steal a ride. Driver, Keith Whittaker, told The Goulburn Post that he’d driven several kilometres when he felt a kick to the back of his seat.

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“I turned around and saw two legs stretched across the back between my seat and the floor. She was lying on the floor,” he said. “I got an extreme shock.”

He described Riana as being in a “catatonic” state; she was reportedly unable to provide any personal details or identify where she was. Whittaker phoned police, and Riana was taken to Goulburn Hospital, where she was treated for stress-related issues.

Jacoba and Mark were reported missing that afternoon, prompting police to attend the family home in Silvan.

Ella arrived there that evening.

Wednesday, August 31.

Mitchell arrived home that morning, having caught the overnight train from Sydney.

Police searched the Jenolan Caves area for the parents, but they were nowhere to be found. They’d already driven back over the Victorian border to the town of Wangaratta.

From there, Jacoba Tromp travelled alone north to Yass (outside of Canberra) on public transport, while Mark remained behind.

That night, a young couple in Wangaratta experienced a disturbing incident in which they were tailgated by a man in a silver Peugeot station wagon. When they pulled over, the driver got out of the car and ran towards them, before stopping in the middle of the road, staring at them, then walking into nearby Merriwa Park. It was believed to be Mark Tromp.

Thursday, September 1.

In an effort to locate his father, Mitchell Tromp appeared on Channel 9 alongside police, appealing for information.

“He’s scared that people are after him; he’s not in a good state of mind,” the 25-year-old told Today.

Who Mark thought those ‘people’ were remains unclear. Mitchell simply told host, Sylvia Jeffreys, that he couldn’t provide a specific explanation for his parents’ paranoia, and that their “extreme” behaviour shocked him.

“I’ve never seen anything like it. It’s really hard to explain or put a word on it but they were just fearing for their lives, and then they decided to flee,” he said.

That afternoon, Jacoba Tromp was admitted to hospital in Yass after a passerby spotted her wandering around the town in an agitated state. According to The Daily Telegraph, Sergeant Mark Knight of NSW Police said doctors at the hospital had assessed her, and her mental health “wasn’t of a good standard”.

Sgt. Knight also referred to the case as the most “bizarre” he’d come across in three decades of policing.

Saturday, September 3.

Mark Tromp was located running along a street on the outskirts of Wangaratta that evening. He was picked up by police, and released to a relative several hours later. As he was driven away, he gave waiting media the middle finger.

In a statement the following week, he expressed his regret over the ordeal but didn’t elaborate on what had caused his distress: “Without reservation, I apologise for the hurt and concern caused by these events,” he said.

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Ella and Mitchell. Image: Sky News.

The theories.

At the time, there was wild speculation about what prompted the Tromp family to flee. Theories ranged from psychosis caused by chemicals used on their redcurrant farm, to suggestion that they were running from debt collectors.

Both were ruled out, and police didn't comment further.

But as it was clear mental ill-health played a significant role, one of the most persistent theories to emerge was that the family may have been experiencing a psychological condition known as folie à deux (madness of two), in which people in close-knit relationships experience a shared psychosis.

Riana appeared to nod to this in her Woman's Day interview.

"You do start thinking the same," she said.

“You have a few things and they do build up — you can get sick in some way."

Her siblings, meanwhile, seemed as baffled as those who'd followed their story.

"It is very confusing, I still feel confused," Ella said during a press conference. "I think our state of minds wasn't in the best place, um, and yeah, I can't even really… There's no one reason for it – it's bizarre."

Mitchell said he couldn't explain what had happened, either. But said he didn't share his father's sense of danger when they scrambled into the car on August 29.

"I just had to go with the family because I wanted to see where they were going. I couldn't leave them," he said. "But, yeah, it was tough to see your family like that, and I've never seen anyone like it, but the main thing is they're OK now. Everyone is safe, everyone is well. So we can just go back to being the family again."

The Tromps have kept a low profile in the nearly three years since, and have seemingly returned to work and their regular lives. Ella was charged with car theft over the incident, but the charges were ultimately withdrawn with the understanding of the vehicle's owner.

If you are struggling with your mental health, crisis support is available 24 hours a day via Lifeline. Please call 13 11 14.